Effects Of The Precipitates On Shape Memory Effect And Corrosion Resistance In A FeMnSiCrNi Alloy

The influence of aging treatment on the shape memory effect and corrosion resistance of a newly developed FeMnSiCr Ni based alloy containing C, N and V elements was investigated. Results showed that V?CN? and Cr₂₃C₆ particles precipitated during aging with the nucleation sites of grain boundaries, dislocations and stacking faults, the amount and size of the particles increased with increasing aging time. The effects of the V?CN? and Cr₂₃C₆ second phases particles on microstructure, shape memory and corrosion resistance were systematically studied.After aging, the shape memory effect was significantly improved. A sharp increase of shape recovery ratio occured in the aging time from 0 h to 4 h, over which aging had little effect on shape memory effect. With the aging time prolonging, the shape recovery ratio increased slightly and steadily, and reached its maximum value at 24 h.The second phases played the key role in the corrosion behavior of the newly developed shape memory alloy. The corrosion behavior in 0.5 M H₂SO₄ solution was almost same for all the samples, barring a slight difference in the passivation range. In addition, the passivation current and critical current required for onset of passivation of the aged samples were almost triple that of the unaged. In 3.5% NaCl solution the corrosion behavior of all aged samples was that of general dissolution with localized attack?pitting?, which can be attributed to the micro-cathodic effect of the V?CN? and Cr₂₃C₆ particles precipitated during aging. Although the best corrosion resistance in both H2SO4 and 3.5% NaCl solutions was shown by the solution treated sample, 24 h-aged sample exhibited an improved corrosion resistance, ascribed to the improved chemical homogeneity of the austenite matrix due to long aging time?24 h?.